1. Field of the Invention
The present invention relates generally to the field of power supply regulators, and, more specifically, to power supply regulators for microelectronic equipment.
2. General Background and Related Art
As the speed and performance of microelectronics devices have continued to increase, so too have the input power requirements for these microelectronics devices continued to increase. Such microelectronics devices include, for example, a microprocessor device utilizing a processor die embodied in an integrated circuit. However, it is desirable to reduce input power requirements from an engineering perspective in order to limit power consumption and to permit relatively smaller form factors still capable of providing the required heat dissipation. Therefore, techniques have been developed for reducing input power requirements while maintaining and increasing processing performance and speed.
For microprocessor devices, for example, reduction in the Central Processing Unit (CPU) supply voltage has been a widely employed technique used to achieve a reduction in power consumption. Another technique includes providing microelectronics devices designed to operate using multiple supply voltages in order to reduce the overall total power consumption of the device. One such technique in particular involves providing a microelectronics device (for example, a single processor die) designed for operation with either of two different input voltage ranges.
The amount of permissible deviation in the input supply voltage is a critical parameter in the design of microelectronics devices. The choice of design techniques and circuit configurations to be used in realizing the design of the microelectronics device may be limited due to a particular input supply voltage tolerance specification. Furthermore, if the input power (voltage or current) is not maintained within its required tolerances (also known as “out of regulation”), the behavioral characteristics of the microelectronics device's circuitry may be adversely affected to cause a variety of unwanted behaviors, including device latchup or transitions into indeterminate states. For at least these reasons, it is desirable to maintain input power voltage and current within specified tolerances. Toward this end, power supply regulators are used to maintain input power received from a power source such as, for example, a battery or a loosely regulated source, within the required design tolerances.
The amount of permissible deviation in input voltage in particular may be expressed as a percentage tolerance centered at a particular voltage level. For example, an input voltage specification may require an input voltage VCC to be +2 VDC±10%. In other words, the input voltage must be maintained by a regulator to within 10% of +2 VDC in order to be considered within regulation.
Microelectronics devices designed to utilize two or more input voltage specifications may present particularly challenging design issues. One such challenge is that the actual amount of permissible deviation in the input voltage may become smaller, or tighter, as the required input voltage level is reduced. Thus for the lower of the two (or more) input voltage levels, the permissible deviation of the input voltage can be significantly tighter than for the larger input voltage level(s), even as microcircuit devices demand increasing amounts of input current, ICC, at the lower VCC.
FIG. 1 is an exemplary illustration of the relatively tighter tolerance required to be maintained “in regulation” for the lower of two input voltage requirements. Referring to FIG. 1, in order to provide regulated input power for a given microelectronics device at a nominal voltage of VCC, under any load conditions the input voltage is required to be within a tolerance of, for example, a 10% VCC window, or VCCmin≧90%*VCC. Such a scheme is typically employed to limit the excursion of the supply voltage to a small window. As for an upper limit, device reliability may be reduced if the supply voltage presented to the microelectronics device rises above VCCx, a reliability limit voltage level greater than VCC nominal. The 10% window required for voltage regulation places a heavy burden on the power supply and power delivery system to meet a tight dynamic impedance range (ZDYN—1) for a given current step, as impedance reduces linearly as the supply voltage decreases or load current increases.
The exemplary voltage values depicted in FIG. 1 are shown in an example for a dual VCC system. As shown in FIG. 1, in the case of the higher supply voltage (VCC=2.0 VDC) the regulation window available, or range, is about 200 mV whereas the regulation window decreases to 140 mV at the lower input voltage level of 1.4 VDC. As the microelectronics device supply voltage drops to the sub ˜1 Volt range, the regulation window increasingly becomes a critical design issue. In particular, the stringent tolerance requirement on the lower input voltage may be the cause of design difficulties and significantly increased product cost due to design constraints for avoiding electrical phenomena such as droops using decoupling effects, and also due to the increased circuitry required to regulate the input voltage to within such fine tolerances. In the environment of multiple input voltage required values, this problem may be exacerbated by, for example, static and transient voltage “droop” characteristics occurring for the lower VCC input voltage required value when the microelectronics device demands relatively high supply current. Voltage droop describes a situation in which the input voltage provided by the regulator to the microelectronics device moves toward or is presented at a voltage level that is lower than the specified input voltage required value but is still within the specified tolerance level to maintain supply voltage in regulation.